Soft tissue anchors and systems for implantation

ABSTRACT

A soft tissue anchor implantation device having a bore along its longitudinal axis through which a guiding K-wire or other guiding devices may be freely drawn, and into which an anchor expanding pin may be wedged to expand the anchor body and lodge it securely in a hole in a bone. In one embodiment the anchor has an elongated body with proximal and distal ends. The proximal end is supplied with an enlarged head having an underside equipped with downwardly extending spikes for gripping soft tissue.

This is a division of application Ser. No. 08/058,631 filed May 6, 1993,now U.S. Pat. No. 5,380,334 which is a continuation-in-part of U.S. Ser.No. 08/018,449 filed Feb. 17, 1993, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is of a system for implanting soft tissue anchors forholding soft tissue in place relative to bone. More particularly, theinvention provides a system for readily implanting soft tissue anchorsas well as soft tissue anchors that are equipped with structuralfeatures preventing their inadvertent withdrawal from bone holes.

2. Description of the Related Art

In the field of surgery it is sometimes necessary to perform operationsto reattach soft tissue to bone. For example, U.S. Pat. No. 4,924,865describes a repair tack designed for use in arthroscopic surgery torepair a torn meniscus in the knee. Reattachment of soft tissue to bonemay also arise, for instance, when surgery is performed on a shoulder toremove or repair glenohumeral tissue.

Regardless of the circumstance, whenever bone must be reattached totissue, it is desirable to have a fastener or "anchor" that will holdthe tissue onto the bone at its point of reattachment, and that willallow the tissue to heal and naturally reattach itself to the bone.Thus, it is desirable that the soft tissue fixation element should notinterfere with the healing process and should allow progressivelyheavier loads to be placed on both bone and soft tissue to encouragehealing and development of attachment strength.

U.S. Pat. Nos. 4,590,928 and 4,851,005 disclose surgical implants thatinclude an expandable stud and a pin for insertion into the stud toexpand the stud. The stud and pin are both fabricated from biodegradablepolymeric materials, and include carbon fibers aligned along theirlongitudinal axes. The stud body has an enlarged head at one end and, atthe opposite end, its cylindrical surface is longitudinally split.Further, the stud has a cylindrical bore running throughout its lengthalong its longitudinal axis. The pin is inserted into this bore therebyforcing the split distal ends radially outwards, to expand the stud bodyand lodge it firmly in a hole in bone. The stud and pin combination isused to connect a synthetic flexible cord for holding two bones togetherin a mammalian body.

Likewise, U.S. Pat. 4,834,752 is directed to a "tissue augmentationdevice" for repairing ligaments or tendons. The device includes at leastone strap-like element (substitute tendon) formed of stablebiocompatible material and a biodegradable element for connecting thestrap-like element to bone. The biodegradable fasteners shown in FIGS. 2and 4 of the '752 patent, include a pin having a longitudinal body witha head at one end, a longitudinal bore through the body, and slits atthe distal end of the body producing longitudinal distal segments. A pinis insertible into the bore of the body for expanding the segmentsradially outward so that they will grip the sides of a hole in bone. Theembodiment of FIG. 4 shows barbs extending downward from theundersurface of the head for engaging the strap-like element and holdingit in place.

EPO Application No. 0 409 364 shows a conical-shaped implant for joiningtogether bone fragments. The longitudinal body of the implant issupplied with a conical axial hole, and a pin for inserting into thehole to expand the body of the implant, and wedge it firmly insurrounding bone tissue. The implant is bioresorbable to eliminate theneed for later surgical removal. The outer surface of the implant isequipped with barb-like projections, presumably for assisting in holdingthe implant in place in the bone hole.

U.S. Pat. Nos. 4,590,928 and 4,851,005, likewise show an expandable studfor attaching a flexible cord, of biocompatible fibers in abiocompatible matrix, to bone. The stud has a longitudinal body with ahead a one end, a bore extending along its longitudinal axis, and issplit at its distal end to form separate legs so that when a pin isplaced within the bore, it expands the legs radially outward to wedgethe stud firmly in a hole.

What is yet needed is a surgical implantation kit that allows easy,accurate implantation of soft tissue anchors at desired bone-soft tissuecontact points. The implanted anchors should grip soft tissue againstthe bone to promote rapid attachment and should decrease its grippingstrength over time to gradually reduce stress shielding there byshifting stress loads to the soft tissue-bone interface so that theinterface strengthens as it heals. Further, the anchors should berelatively small, to avoid drilling large holes in bone and soft tissuethat increase healing time, but at the same time should resist beingpulled out of the bone hole by applied forces.

SUMMARY OF THE INVENTION

The invention provides a surgical kit for the implantation of softtissue-to-bone anchors, and expandable soft tissue-to-bone anchor studs.

In one embodiment, the invention surgical implantation kit includes ahollow outer tube with a distal end to which is releasably orthreadingly attached a soft tissue anchor, with its longitudinal axisaligned with the longitudinal axis of the outer tube. The soft tissueanchor has a bore along its longitudinal axis, through which a guidingK-wire or other guiding means may be freely drawn, and into which ananchor expanding pin may be wedged to expand the anchor body and lodgeit securely in a hole in bone. The surgical implantation kit alsoincludes a longitudinal inner tube, sized to fit within the hollow boreof the outer tube. An anchor pin, for expanding the anchor body, isfrictionally held at the distal end of the inner tube. A pushrod, sizedto fit within the inner tube, is supplied with means for gripping andapplying leverage to force the anchor pin from the inner tube into thebore of the soft tissue anchor stud. This is achieved by nesting theinner tube into the outer tube. The inner tube has the anchor pin at itsdistal end and the pushrod inserted into its proximal end. Applyingforce to the pushrod forces the anchor pin into the bore of the anchorstud to wedge the stud in the bone hole.

In order to insert an anchor stud using the surgical implantation kit ofthe invention, soft tissue to be connected to bone is drawn intoposition across the surface of the bone to which it must be attached.This may be done by grasping or skewering the soft tissue with the tipof the K-wire. A suitable location for tacking the soft tissue to thebone is then selected. A hole is drilled through the tissue and into thebone at the selected location to the desired depth, using a cannulateddrill with a K-wire, or other guide means, inserted into the drillcannula. When the hole has been drilled to a predetermined depth, thedrill is removed but the K-wire or other guide means is retained inplace. The soft tissue anchor and the outer tube of the inventionimplantation apparatus are then placed around the implanted K-wire. Inthis manner, the anchor is guided into place in the drilled hole. Whenthe anchor is in position, the K-wire or other guide means is removed.In one embodiment, the inner tube is then placed inside the outer tubeand the anchor-expanding pin at the distal end of the inner tube isguided and pushed into the anchor stud by depressing the pushrod whichis nested in the inner tube, causing the anchor to expand so that itssides tightly grip the sides of the hole. When the anchor pin has beenfully inserted, the outer tube can be released, sheared from, orthreadingly disengaged from the inserted anchor.

In another embodiment, the surgical implantation kit includes an outertube with an anchor stud releasably held at its distal end and acannulated plunger designed to fit within the inner tube. The anchor pinis releasably held on the distal end of the plunger and is pushed intothe anchor stud when the plunger is depressed. To insert an anchor stud,a hole is drilled as described above and the K-wire is passed throughthe cannulation of the anchor stud, into the outer tube, and thenthrough the cannulation of the plunger. Thus, the anchor stud is guidedinto the hole. When the anchor stud is in place in the bone hole and theK-wire is removed, the plunger is depressed to guide and force theanchor pin into the communicating bore of the anchor stud. When the pinhas entered and expanded the anchor stud, the outer tube containing thepushrod can be disconnected from the anchor stud and the plunger can bereleased from the anchor pin.

The invention also provides specific soft tissue anchor stud designsthat are not easily removed from the hole in the bone. Further, the softtissue anchors are preferably comprised of a bioabsorbable polymericcomposition designed so that, as the bone and tissue heal together, theanchors will gradually bioabsorb thereby transferring stress to theattachment point and facilitating healing while minimizing stressshielding.

In particular, in one embodiment the invention soft tissue anchor studcomprises an elongated body portion having distal and proximal ends. Theproximal end is supplied with an enlarged head having an undersideequipped with downwardly extending spikes for gripping soft tissue. Theunderside surface of the head is preferably also angled at an angle β tothe horizontal so that soft tissue is gripped between the spikes and theangled undersurface which form a pinch point for gripping soft tissue.

Typically, the soft tissue anchor is inserted into a hole which isdrilled at an angle of up to 30° from the perpendicular in the bone.Thus, under ordinary circumstances, when the bone hole is angled, onlythe spikes on one side of the anchor will tightly engage soft tissue.The downwardly extending spikes on the other side may only lightlyengage tissue.

In a second embodiment, the anchor stud does not have an enlarged headbut instead is equipped with sutures attached to or embedded in theanchor body that can be used to affix soft tissue to an anchor wedged ina bone hole.

In an alternative embodiment, the anchor stud has an enlarged headtilted at an angle γ, approximating the angle to the perpendicular atwhich a hole is drilled into the bone. Thus, the tilt angle of the headpermits downwardly extending spikes located on the underside of the headto engage soft tissue and hold the soft tissue firmly, but withoutinducing necrosis, between the underside of the head and the bonesurface. This tilt-headed anchor stud is also expandable in that it issupplied with a longitudinal bore into which an expanding pin may beinserted to radially outwardly expand expandable legs of the anchorstud.

A longitudinal bore extends along the longitudinal axis of theinvention's soft tissue anchors passing through their distal end. At thedistal end, the soft tissue anchors have several legs, extendingparallel with the longitudinal axis and radially outwardly expandablewhen an anchor pin is inserted into the longitudinal bores of theanchors. This radial outward spreading of the legs forces the legsagainst the sides of a bone hole and wedges the anchor studs securely inthe hole.

To further assist in wedging the invention's anchor stud in place, theoutside surface of the legs are provided with barb-like projections forengaging bone. These bone-engaging barbs counteract forces acting alongthe longitudinal axis of the anchor to withdraw the anchor from the bonehole. Further, on the upper or proximal portion of the outer surface ofthe anchor body, there are provided a series of "bending barbs" eachplaced so that they do not impede insertion of the anchor, and do notdamage the bone tissue by broaching away bone that other bending barbsmust later engage. These bending barbs resist forces acting at an angleto the longitudinal axis of the anchor body to remove the anchor fromthe bone. Specifically, these angled forces cause the anchor to bendslightly in the hole thereby forcing the bending barbs to engage bonetissue and thereby preventing the withdrawal of the anchor from the bonehole.

The invention anchor stud and pin for expanding the anchor stud may bemade of any biocompatible polymer. Suitable nonbioabsorbablebiocompatible polymers include ultra high molecular weight polyethylene(UHMWPE) and the like. Bioabsorbable polymers are preferred for certainapplications and include polylactic acid, polyglycolic acid, copolymersthereof, and the like.

The invention provides surgical soft tissue anchor implantation kitsthat are easy to use for the implantation of any expandable soft tissueanchors in any surgical operation where it is desired to anchor softtissue or soft tissue substitute, such as a synthetic ligament, to bone.Further, the invention provide specific types of soft tissue anchorsthat are bioabsorbable, expandable, and that resist withdrawal forcesacting on the anchors.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing "detailed description of the preferred embodiments" isconsidered in conjunction with the following drawings which are not toscale and in which significant features have been exaggerated to showdetail.

FIG. 1 is a schematic diagram of an embodiment of the invention systemfor the implantation of an expandable soft tissue anchor.

FIG. 1A is a schematic enlarged view of a distal portion of the innertube of FIG. 1 showing the anchor pin held in place.

FIG. 1B is a cross-sectional view of FIG. 1A taken at B--B.

FIG. 2 is a schematic diagram of an embodiment of the invention softtissue anchor with the left hand side in the "expanded position" andright hand side in the non-expanded, or "insertion position."

FIG. 3 is a schematic diagram of an embodiment of the invention softtissue anchor showing its attachment to the distal end of an outer tube.

FIG. 3A is a schematic diagram of a cross section taken of FIG. 3 atA--A.

FIG. 4 is a schematic diagram showing an embodiment of the inventionsoft tissue anchor implanted in bone and gripping soft tissue.

FIG. 5 is a schematic diagram of an embodiment of the soft tissue anchorstud implanted in bone.

FIG. 6 is a schematic depiction of an anchor stud with a tilted head andlegs radially outwardly expandable.

FIG. 7 is a schematic diagram of an embodiment of a system forimplantation of an expandable soft tissue anchor.

FIG. 7A is a cross-section along B--B of FIG. 7 showing the anchorexpanding pin held by the outer tube by friction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiment of the invention surgical kit for implantationof a soft tissue anchor may better be understood with reference toFIG. 1. A soft tissue anchor 4 is attached to the distal end 3 of anouter tube 2, which also has a proximal end 1. The outer tube is hollowand has a longitudinal bore 10 extending along the entire length of theouter tube 2. The distal end of the outer tube 3 is releasably orthreadingly connected to the upper surface of the head 11 of soft tissueanchor 4. An anchor bore 12, coextensive with and communicating withouter tube bore 10, extends longitudinally through soft tissue anchor 4from its proximal extremity to its distal extremity. The distal end 13of anchor stud 4 includes at least two separate legs 22, each outwardlyexpandable when an anchor pin, sized to fit snugly within the bore ofthe soft tissue anchor, is positioned within the bore of soft tissueanchor 4.

An inner tube 6, sized to fit within the bore 10 of outer tube 2, isequipped with a releasably held anchor pin 8, as shown in FIGS. 1A andlB. With reference to FIG. 1A, a segment of inner tube 6 is slithorizontally at four places thereby producing segments 50. Thesesegments are resilient and two opposing segments can be depressed inwardtowards the longitudinal axis of bore 9 of inner tube 6. Thus, thedepressed segments 50 create a pinch point of sufficient clamping actionto hold anchor pin 8 in place. When the anchor stud 4, releasably heldat the distal end 3 of outer tube 2 has been implanted in the bone hole,then inner tube 6 is inserted into the bore 10 of outer tube 2 andpushrod 30 is inserted into the bore 9 of inner tube 6. Pushrod 30 isthen depressed by pushing on leveraging means 31 while holding grippingmeans 5. This depressing of pushrod 30 releases anchor pin 8 from thepinch point of segments 50 and guides the pin down the bore 9 to thecommunicating bore in anchor stud 4 into which the anchor pin 8 is thenforced by pushrod 30 thereby expanding legs 22 of stud 4 radiallyoutward to hold the stud in place. When the anchor pin 8 has beeninserted into the soft tissue anchor, then the outer tube can bereleased from or threadingly disengaged from the implanted soft tissueanchor. The release of the outer tube 2 from the anchor stud 4 may beachieved by shearing a connection of predetermined strength between thetwo devices, by unscrewing one from the other, or by other means.

In an alternative embodiment, the surgical implantation kit does notrequire an inner tube. With reference to FIG. 7, showing thisalternative embodiment, a plunger 40 is desirably permanently engagedwithin an outer tube 2. The outer tube 2 has an anchor stud 4 releasablyengaged at its distal end 3. This releasable engagement may be achievedby screw threads cooperating between distal end 3 and the head 8 ofanchor stud 4. Alternatively, the anchor stud may be releasably held byfriction or may be engineered for attachment with the distal end of thetube with a predesigned weakening at the point of attachment so that thedistal end 3 may be separated cleanly from the head 8 upon applicationof an appropriate amount of force. In this embodiment, plunger 40 has ananchor pin 8 releasably attached to its distal end. As shown, the distalend of the plunger pushes against pin 8 at point 45. See FIG. 7A.Further, plunger 40 is preferably fabricated and assembled so that thesurgical implantation unit presented to the user has plunger 40 alreadyinserted into outer tube 2, as shown in FIG. 7. A segment of the plunger40 is extended so that, in the plunger depressed position point 45 isbelow the head 18 of the anchor 4. In order to use this embodiment ofthe implantation kit, a hole is drilled in the usual manner and theK-wire used for guiding insertion of the anchor stud is inserted throughthe anchor stud 4, into the cooperating bore of outer tube 2, and theninto the bore 43 of plunger 40. When the anchor stud 4 has beenpositioned within the bone hole, the K-wire is removed and plunger 40 isdepressed using depression means 42 and outer tube gripping means 5.Upon depression of plunger 40, anchor pin 8 is forced into the bore ofanchor stud 4, expanding the anchor stud into place in the bone hole. Atthis point, cooperating stop means 44 on plunger 40 contacts and isengaged by stop means 41 of outer tube 2. Preferably, the distal end 3of outer tube 2 is internally shaped to guide anchor pin 8 into positionin the bore of anchor stud 4 when pushrod 40 is depressed.

The above-described surgical systems for implantation of soft tissueanchors can be used with any design of soft tissue anchor that issupplied with a bore for expanding the body of the anchor to wedge theanchor securely in a bone hole. The anchors may be fabricated frombioabsorbable or nonbioabsorbable polymeric compositions, and otherbiocompatible materials. The soft tissue anchor may, for instance, besupplied with a smooth cylindrical body or shaft, or may have barbsextending from the shaft, as shown in the invention soft tissue anchorof FIG. 2. Further, the soft tissue anchors useful with the invention'ssurgical implantation kit may or may not include sharp-edged barbsdownwardly extending from the undersurface of the head of the anchor forgripping soft tissue. Indeed, useful anchors need not have an enlargedhead.

An embodiment of the invention's soft tissue anchors is shown in FIGS.2, 3, and 3A. From FIG. 2, the soft tissue anchor 4 has an enlarged head18, with an upper surface 11, and an undersurface 17. The undersurface17 is at an angle β to the horizontal. This has significant implicationsbecause the anchor is normally placed in a hole drilled at an angleabout β (about 15°) to the horizontal. Consequently, only about one halfof the undersurface of the head 18 will intimately and tightly contactsoft tissue when the anchor is in place, as can be seen from FIG. 4where bone is represented by 100 and soft tissue 102. The other half ofthe head undersurface will extend above the soft tissue or will onlymarginally contact the tissue. Soft tissue engaging barbs 14 extenddownwardly from surface 17 and are sized to approximate the thickness ofthe soft tissue to allow such firm embedment in the tissue as is neededwithout inducing necrosis of the soft tissue. The soft tissue anchor hasan elongate body 20 extending downwardly from the head 18. The body hasa proximal end 19 and a distal end 13. A bore 12 extends along thelongitudinal axis of the body 20 and passes through the head 18. Thedistal end of the anchor body 20 is divided into separate legs 22. InFIG. 2, the right hand side leg is shown in a "non-expanded position"before an expanding pin is placed within the bore 12. On the other hand,the left hand side leg 22 is shown in the "expanded position" after ananchor expanding pin has been forced into the bore 12.

The anchor is supplied with barbs 16 shaped to allow ease of insertionbut having sharp upper edges 23 to bite into the bone and resistwithdrawal, when a withdrawal force is applied along the axis of theanchor in the direction P. Further, the proximal half 19 of the outersurface of the soft tissue anchor is supplied with "bending barbs" 15,each positioned on the anchor circumference so as not to broach boneaway from the next succeeding barb. These sharp, low profile barbs 15are designed to engage trabecular bone structure when the anchor is bentslightly. This bending usually occurs when forces are applied to pullthe anchor from its implanted position in the bone hole. Typically, theangle of applied force α is about 15° to about 45° off the perpendicularaxis of the anchor stud. When force is applied at the angle α, then theanchor, because it is flexible, tends to bend slightly. When thisbending occurs, the "bending barbs" 15 engage trabecular bone structureand oppose withdrawal of the anchor 4 from its position in the hole. Thepositioning of the barbs 15 around the circumference or outer surface ofthe proximal portion 19 of the soft tissue anchor 4 can most easily beseen with reference to FIG. 3A.

An alternative embodiment of the invention soft tissue anchors is shownin FIG. 5. In this embodiment, the soft tissue anchor does not includean enlarged head with an angled undersurface and downwardly extendingspikes. Instead, sutures 40 are embedded or fixedly attached to theexpandable anchor. These sutures 40 may be used to affix soft tissue tobone 100 or for other purposes, as needed. In this embodiment, theanchors include barbs 16 to counteract forces withdrawing the anchorfrom its implanted position, and bending barbs 15 to resist withdrawingforces applied at an angle to the longitudinal axis of the anchor stud.

A further alternative embodiment of the invention soft tissue anchors isshown in FIG. 6. In this embodiment, the head 8 is tilted at an angle γto the horizontal so that when the anchor is implanted, the undersurfaceof the head fits flushly against soft tissue 102 while downwardlyextending spikes 14 engage body tissue. In this manner, unlike thetypical untilted head shown in FIG. 4, the soft tissue anchor is moreeffective in holding soft tissue in place. Whereas the soft tissueanchor of FIG. 6 is supplied with barbs 16 on outwardly expandable legs22, the soft tissue anchor may also be further equipped with bendingbarbs, in a manner similar to that shown for the embodiment of FIG. 4.The angle γ is from about 10° to about 30°, preferably about 20°.

The invention soft tissue anchors can be used in conjunction with thesoft tissue anchor surgical implantation kit described above. FIG. 3shows the connection between the distal end 3 of outer tube 2 with head18 of anchor 4. In this particular embodiment, the outer tube distal end3 is insert molded into the head 18 and is held in place by grippingmeans 24 interacting with a groove or cooperating means in head 18. Theanchor pin 8, sized to the approximate length of the anchor body 20 andhead 18, is inserted into bore 12 from the head of the anchor and isforced to the distal end of the anchor 13, thereby expanding legs 22radially outward to grip the sides of the bone hole.

The method for implanting soft tissue anchors using the invention'ssurgical implantation devices requires firstly positioning the softtissue over the segment of bone to which it must be attached. WithK-wire locked into the cannulated drill and extending about 1/4 inchbeyond the drill tip, the soft tissue is skewered and moved intoposition over the bone. The drill is then used to drill a hole to apredetermined depth in the bone. Thereafter, the drill is removed withthe K-wire, or other guide means, remaining in place in the hole so thatthe free end is inserted into the distal end 13 of anchor 4 and into thebore 10 of tube 2. This allows guiding of the anchor 4 through the softtissue and into the bone hole. When the shaft 20 of the anchor is firmlyplaced in the hole, then in the embodiment of FIG. 1, the inner tube 6is inserted into outer tube 2 and pushrod 30 inserted into inner tube 6.The pushrod 30 is pushed with gripping and leverage means 31 until theappropriately sized anchor pin 8 enters the bore 12 in anchor 4 therebyradially outwardly expanding legs 22 so that gripping barbs 16 and edges23 tightly engage the sides of the bone hole. Once this has beenachieved, outer tube 6 can be released from the anchor 4, leaving thelatter in place in the bone hole, tightly gripping the soft tissue. Themethods of using other embodiments of the implantation kit are discussedfully above.

The foregoing disclosure and description of the invention areillustrative and explanatory thereof, and various changes in the size,shape, materials, as well as in the details of the illustration may bemade without departing from the spirit of the invention as disclosedabove and claimed below.

What is claimed is:
 1. A surgical implant for anchoring soft tissue tobone, the implant comprising:(i) a radially-outward expandable anchorstud for inserting in a hole in bone, the stud having proximal anddistal ends and an elongate body with an outer surface and alongitudinal axis;the stud further comprising:(a) a longitudinal boreextending along the longitudinal axis for receiving a stud-expandingpin; (b) at least two radially-outward expandable legs on the distal endof the stud for gripping sides of a bone hole; (c) a plurality of barbson the outer surface of the elongate stud for gripping the sides of abone hole and resisting forces in the direction of withdrawing the studfrom the bone hole; and (d) an enlarged head at the proximal end of thestud, the enlarged head having an undersurface at an angle β relative toa plane perpendicular to the longitudinal axis and comprising aplurality of downwardly extending spikes for engaging soft tissuebeneath the undersurface; and (ii) a stud-expanding pin for inserting inthe longitudinal bore of the stud body to expand the at least two legsradially outward for gripping the sides of a bone hole.
 2. The implantof claim 1, wherein the angle β is about 15°.
 3. The implant of claim 1,wherein the anchor stud and anchor expandable pin comprise abioabsorbable polymeric composition selected from the group consistingof polylactic acid, polyglycolic acid, and copolymers thereof.
 4. Theimplant of claim 1, wherein the barbs comprise bending barbs on aproximinal segment of the outer surface of the elongate stud body, eachof the bending barbs extending across only a segment of a circumferenceof the anchor stud body without said segments overlappingcircumferentially.
 5. The implant of claim 4 comprising from about 8 toabout 16 bending barbs.
 6. The implant of claim 1, wherein the barbscomprise gripping barbs on a distal segment of the outer surface of theelongate stud body.
 7. The implant of claim 6 comprising about fourgripping barbs.
 8. The implant of claim 1, wherein the barbs comprisecombination of bending barbs on a proximal segment of the outer surfaceof the elongate stud body and gripping barbs on a distal segment of theouter surface of the elongate stud body, each of the bending barbsextending across only a segment of a circumference of the anchor studbody without said segments overlapping circumferentially.
 9. The implantof claim 8 comprising from about 8 to about 16 bending barbs and aboutfour gripping barbs.
 10. The implant of claim 1, wherein the barbscomprise bending barbs on a proximinal segment of the outer surface ofthe elongate stud body, each of the bending barbs extending across onlya segment of a circumference of the anchor stud body without saidsegments overlapping circumferentially.
 11. The implant of claim 10comprising from about eight to about sixteen bending barbs.
 12. Theimplant of claim 1, wherein the barbs comprise gripping barbs on adistal segment of the outer surface of the elongate stud body.
 13. Theimplant of claim 12 comprising about four gripping barbs.
 14. Theimplant of claim 1, wherein wherein the barbs comprise combination ofbending barbs on a proximal segment of the outer surface of the elongatestud body and gripping barbs on a distal segment of the outer surface ofthe elongate stud body, each of the bending barbs extending across onlya segment of a circumference of the anchor stud body without saidsegments overlapping circumferentially.
 15. The implant of claim 14,wherein the anchor stud and stud-expanding pin comprise a bioabsorbablepolymeric composition selected from the group consisting of polylacticacid, polyglycolic acid, and copolymers thereof.
 16. A surgical implantfor anchoring soft tissue to bone, the implant comprising:(i) aradially-outward expandable anchor stud for inserting in a hole in bone,the stud having proximal and distal ends and an elongate body with anouter surface and a longitudinal axis, said stud comprising:(a) alongitudinal bore extending along the longitudinal axis for receiving astud-expanding pin; (b) at least two radially-outward expandable legs onthe stud for gripping sides of the bone hole; (c) a plurality of bendingbarbs on a proximal segment of the outer surface of the elongate studbody for gripping the sides of the bone hole and resisting forces,applied at an angle to the longitudinal axis, to prevent withdrawal ofthe stud from the bone hole; and (d) gripping barbs on a distal segmentof the outer surface of the elongate stud body for holding the stud in abone hole; (ii) a stud-extending pin for inserting in the longitudinalbore of the stud body to expand the at least two legs radially outwardfor gripping the sides of a bone hole; and (iii) elongate suturesembedded in a proximal end of the anchor stud such that when the anchorstud is inserted into a bone hole, the sutures extend from the hole. 17.A surgical implant for anchoring soft tissue to bone, the implantcomprising:(1) a radially-outward expandable anchor stud, the studhaving proximal and distal ends and an elongate body with an outersurface and a longitudinal axis; the stud further comprising:(a) alongitudinal bore extending along the longitudinal axis for receiving astud-expanding pin; (b) at least two radially-outward expandable legs onthe stud for gripping sides of a bone hole; (c) a plurality of bendingbarbs on a proximal segment of the outer surface of the elongate studbody for gripping bone and resisting forces, applied at an angle to thelongitudinal axis, to prevent withdrawal of the stud from a bone hole;(d) gripping barbs on a distal segment of the outer surface of theelongate stud body for holding the stud in a bone hole; and (e) anenlarged head at the proximal end of the stud, the enlarged head beingtilted to an angle γ to the horizontal, the enlarged head comprising anundersurface having downwardly extending spikes for engaging softtissue; and (2) a stud-expanding pin for inserting in the longitudinalbore of the stud body to expand the at least two legs radially outwardfor gripping the sides of a bone hole.
 18. The implant of claim 17further comprising from about 8 to about 16 bending barbs.
 19. Theimplant of claim 18 further comprising about 4 gripping barbs.
 20. Theimplant of claim 17 wherein the anchor stud and anchor expandable pincomprise a bioabsorbable polymeric composition.